Process for the production of para-(tertiary alkylated)-alkylbenzenes



United States Patent O PROCESS FOR THE PRODUCTION OF PARA-(TER- TIARY ALKYLATED)-ALKYLBENZENES Seymour H. Patinkin, Chicago, and Robert A. Sanford,

Park Forest, 111., assignors to Sinclair Refining Company, New York, N.Y., a corporation of Maine No Drawing. Application October 25, 1955 Serial No. 542,777

8 Claims. (Cl. 260-671) benzenes have produced a mixture of the para-(tertiaryalkyl) alkylbenzene and he meta-isomer. For example, prior art processes for the production of para-(tertiarybutyl)-toluene have produced a mixture of about 93 percent para-isomerand about 7 percent of the meta-isomer. The meta-isomer is extremely diflicult to remove from such a mixture. For certain uses, however, the paraisomer must be utilized in pure form. For example, para-(t-butyl)-toluene can be oxidized to terephthalic acid by means of dilute aqueous nitric acid of a strength up to about 40-percent at a temperature of at least about 450 F. as described and claimed in pending application Serial No. 550,829 filed December 5, 1955 of Emmett H. Burk, Jr., now abandoned. High purity para-isomer produces a terephthalic acid of particular value in the fiber field where singleness of composition is critical. It has been assumed, however, that the 93 percent paraand 7 percent meta-isomer distribution was a limiting value.

We have found that para-(tertiary-alkylated)-alkylbenzenes are obtained in a purity in excess of about 98% and containing 2% or less of the meta-isomer by reacting the alkylbenzene with a tertiary olefin, or a tertiary olefin producing substance, in the presence of a catalyst comprising hydrogen fluoride while controlling the temperature at a low range, i.e. about -35 to 5 C. Thus, we have found that para-(tertiarybutyl)-toluene is produced in a purity in excess of about 98% and containing 2% or less of the meta-isomer by reacting toluene with isobutylene in the presence of 'a catalyst comprising hydrogen fluoride while controlling the temperature at about -35 C. to 5 C.

The process of our invention provides a selective reaction in which valuable para-(tertiary-alkylated)-alkylbenzenes are obtained in good yields and in higher purity than before. The high purity para-isomers are useful in the preparation of valuable compounds such as terephthalic acid which is useful in the production of fibers.

According to the process of our invention, a monoalkylbenzene is reacted with a tertiary olefin in the presence of a catalyst comprising hydrogen fluoride while controlling the temperature between about 35 to -5 C. At higher temperatures, less pure para-isomer is obtained and at lower temperatures conversion rates decrease sharply. The reaction is stopped, for example, by quenching with water, the product washed with water or alkali solution, dried and the products recovered by distillation.

Generally, the catalyst and monoalkylbenzene are mixed and contacted with the tertiary olefin. The manner of contacting is important in that isomerization of the alkylate can occur while the addition of the olefin to the catalyst and aromatic mixture is being completed resulting in lower para-isomer yields. For example, prolonged contact of the alkylate from toluene and isobutylene with the catalyst causes the alkylate to isomerize and approach the equilibrium distribution of about 67 percent metaand 33 percent para-(t-butyl)-toluene. We have found that keeping the olefin concentration low during alkylation and keeping additional contact time after olefin addition to a minimum avoids this undesirable isomerization and results in the production of high yields of high purity para-isomer. Thus, slow addition of the olefin, early quenching of the reaction and early removal of alkylate from contact with the catalyst is preferred procedure. Advantageously, two streams, one containing alkylbenzene and the olefin and the other alkylbenzene and catalyst, are directed into a mixing chamber and after a short contact time discharged into a stream of water to stop the reaction. The molar ratio of alkylbenzene to olefin to catalyst may vary from about 24:0.51.5:0.51. Preferably the ratio is about 3:l:0.75. A minimum of catalyst is employed as this produces higher purity para-isomer. Large amounts of catalyst increase meta-isomer formation. The product is recovered by alkali washing and distillation.

The monoalkylbenzenes useful in the process of our invention are those in which the alkyl group contains from 1 to 3 carbon atoms, for example, toluene, ethyl benzene and isopropyl benzene. The tertiary olefins useful in the process of our invention are those containing 4 to 5 carbon atoms, for example, isobutylene and isoamylene. By the term tertiary olefin as used herein we also mean to include olefin producing substances such as the alkyl halide, alcohol, ether or ester of the corresponding tertiary olefin. For example, t-butyl chloride and t-amyl chloride, t-butyl alcohol and t-amyl alcohol, t-butyl ether and t-amyl ether, and t-butyl ace tate and t-amyl acetate, are useful.

By hydrogen fluoride catalysts we mean unpromoted hydrogen fluoride. Preferably anhydrous hydrogen fluo ride is employed as less concentrated solutions of hydrogen fluoride promote undesirable polymerization at the expense of alkylation.

The process of our invention will be further illustrated by the following examples.

In the examples, toluene was tertiary-butylated with isobutylene in the presence of hydrogen fluoride as a catalyst using the following procedure.

The hydrogen fluoride catalyzed reactions were performed in a three-necked stainless steel flask equipped with a stirrer, copper thermowell and copper inlet tube. Anhydrous HF was used. The olefin was introduced from a small bomb metered through a Fischer-Porter Flowrator and dried in a CaCl drying tower. The weight of isobutylene added to the reaction mixture was determined by the weight loss of the isobutylene bomb. A bath cooled with Dry Ice-isopropanol was used to control reaction temperature. The catalyst was added to the toluene at the reaction temperature and to this stirred mixture, the olefin was bubbled in at a predetermined rate. Reactions were stopped by quenching with ice and Water. The alkylation products were washed with water and NaHCO solution and dried over K CO In subsequent fractionations, K CO was added to prevent residual impurities from causing rearrangement of the alkylates.

A component analysis of each alkylate was obtained from infrared analysis of the distilled products. These analyses along with reaction conditions of two runs at different temperatures are summarized in Table 1. Conversions are based on the amount of isobutylene charged and are given on an absolute basis. The ultimate yield in all cases was close to 100% since no products other than alkylation products were detected.

5 Table I Runs HF, wt. g. (m) 19 (0.95) 22(111 Time of addition of isobutylene, min 67. 5 67. 5 Toluene, wt. g. (m) 415 (4. 5) 415 (4. 5) Isobutylene, wt. g. (m) 80 (1.43) 80. 5 (1.44) Toluene/isobutylene/HF molr 3/1/0. 65 3/1/0. 75 Reaction temperature, C 0 to 2 -20 Conversion, wt. percent based on olefin 98 97 Product Distribution, wt. percent:

p-t-hutylt0luene 92. 5 98+ m-t-butyltoluene 7. 5 2 o-t-butyltoluene. 0. 0

The results tabulated in Table I clearly illustrate the selective reaction that occurs when low temperatures, i.e. below 0 C., are used resulting in high parato meta-isomer ratios. Thus, at 0 C. only 92.5% paraisomer was obtained while at 20 C. more than 98% para-isomer was obtained.

We claim: 1. A method for the production of para-(tertiary alkylated)-alkylbenzenes which comprises reacting a monoalkylbeuzene in which the alkyl group contains from 1 to 3 carbon atoms with a tertiary olefin con taining from 4 to 5 carbon atoms in the presence of a catalyst comprising hydrogen fluoride while controlling the temperature at about 20 C.

2. The method of claim 1 in which the alkylbenzene is toluene.

3. A method for the production of para-(tertiarybutyl)-toluene which comprises reacting toluene with isobutylene in the presence of a catalyst comprising hydrogen fluoride while controlling the temperature at about 20 C.

4. The method of claim 3 in which the catalyst is anhydrous hydrogen fluoride.

5. A method for the production of para-(tertiaryalkylated)-alkylbenzenes which comprises reacting a monoalkylbenzene in which the alkyl group contains from 1 to 3 carbon atoms with a tertiary olefin containing from 4 to 5 carbon atoms in the presence of a catalyst comprising hydrogen fluoride while controlling the temperature at about minus 20 C. and the molar ratio of alkylbenzene to olefin to catalyst at about 2-4:O.51.5:0.5-l.

6. The method of claim 5 in which the alkylbenzene is toluene.

7. A method for the production of para-(tertiarybutyl)-toluene which comprises reacting toluene with isobutylene in the presence of a catalyst comprising hydrogen fluoride while controlling the temperature at about minus 20 C. and the molar ratio of toluene to isobutylene to catalyst at about 24:0.5-1.5:0.51.

8. The method of claim 7 in which the catalyst is anhydrous hydrogen fluoride.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD FOR THE PRODUCTION OF PARA-(TETIARYALKYLATED)-ALKYLBENZENES WHICH COMPRISES REACTING A MONOALKYLBENZENE IN WHICH THE ALKYL GROUP CONTAINS FROM 1 TO 3 CARBON ATOMS WITH A TERTIARY OLEFIN CONTAINING FROM 4 TO 5 CARBON ATOMS IN THE PRESENCE OF A CATALYST COMPRISING HYDROGEN FLUORIDE WHILE CONTROLLING THE TEMPERATURE AT ABOUT-20*C. 